The Sims 4's Teenagers have a lot of freedom. They gain some special social commands that will not last into adulthood, but otherwise they are more or less like adults. Any Child Skills they possessed are lost, but their equivalent adult skills will gain a boost.
This is where the difference between Generation 1 and Generation 2 Sims really starts to come into play. When we were Getting Started with Christine National, we had to endure the fact that she had zero Skills of any type. We saw her cook her first meal and fix her first appliance as a young adult. For Anna, she'll already have some practice before the skills are absolutely necessary. She can practice cooking, handiness, and other skills that will be essential once (or if) she moves out. Plus, she can slowly start to chip away at her Aspiration, a luxury that Christine did not entirely have time for.
The cosmetic options for Anna grow as well now that she's an adult. She can choose from the full range of clothing, unlike children. Unlike in previous versions of the franchise, whatever clothes Anna uses as a teenager will be the same outfits she'll have as an adult.
More detailed phenotypes also come into play as a teenager. As a Baby, Anna's face was pretty set. As a Child, Anna's face was altered based on the genes of her parents, but she always had the same body type. Now as a teenager, Anna's body even changes based on her parents' shapes. Anna inherits the wider hips and rounder buttocks that we gave Christine during Create, while still inheriting a few features from Freddie as well.